This section provides background information related to the present disclosure which is not necessarily prior art.
Lead is a common ingredient in copper alloys to improve their machinability. Typical lead contents in machinable brass alloys range from about 1 to about 6 percent (by weight). Because of their excellent machinability, these lead-containing copper alloys have been an important basic material for a variety of articles such as water faucets, and supply/drainage metal fittings and valves.
However, the application of these lead-containing alloys has been limited in recent years, because the lead contained therein is believed to be an environmental pollutant harmful to humans. One aspect is the lead contained in metallic vapor that is generated in the manufacturing and processing of these alloys at high temperatures, such as in melting and casting operations. Another aspect is the concern that lead contained in water system metal fittings, valves, and other components made of those alloys will dissolve out into the water supply.
For these and other reasons, many countries have been reducing the permissible levels of lead in plumbing fixtures. While there are a number of copper alloys that can be used, most of these alloys are very difficult or expensive to machine into satisfactory plumbing parts. Various attempts have been made to provide copper alloys with improved machinability for these applications. One good example of such an alloy is C87850, which has a nominal composition of 74-78 weight percent copper, up to 0.1 weight percent antimony, up to 0.1 weight percent iron, up to 0.09 weight percent lead, up to 0.1 weight percent manganese, up to 0.2 weight percent nickel, between 0.05 and 0.2 weight percent phosphorus, between 2.7 and 3.4 weight percent silicon, up to 0.3 weight percent tin, and the balance zinc. Several patents cover C87850 and related alloys, including U.S. Pat. Nos. 6,413,330, 7,056,396, and 7,883,589. These patents teach that for copper contents <70 weight percent “the addition of less than 2.0 percent, by weight, of silicon cannot form a gamma phase sufficient to provide industrially satisfactory machinability.” They further teach that a minimum copper content of about 69 weight percent is needed to provide a satisfactory alloy.
While these alloys provide excellent properties for plumbing and other applications, are readily machinable, and they include little to no lead, these alloys can be relatively expensive to manufacture.